The CData Excel Add-In for ServiceNow supports standard SQL joins like the following examples.

Inner Join

An inner join selects only rows from both tables that match the join condition:

SELECT incident.close_notes, system_user.name FROM incident INNER JOIN system_user ON incident.caller_id = system_user.system_id

Left Join

A left join selects all rows in the FROM table and only matching rows in the JOIN table:

SELECT incident.close_notes, system_user.name FROM incident LEFT JOIN system_user ON incident.caller_id = system_user.system_id